Crash on startup with Postgres - constraint "fk_flow_user_id_user" for relation "flow" already exists

[devinbost]

Bug Description

LangFlow is crashing on startup when postgres is enabled. It's giving this exception:

[12/19/24 18:47:43] ERROR    2024-12-19 18:47:43 - ERROR    - b2fa308044b5_add_unique_constraints - Error during upgrade: (psycopg2.errors.DuplicateObject)    b2fa308044b5_add_unique_constraints.py:51
                             constraint "fk_flow_user_id_user" for relation "flow" already exists                                                                                                       
                                                                                                                                                                                                        
                             [SQL: ALTER TABLE flow ADD CONSTRAINT fk_flow_user_id_user FOREIGN KEY(user_id) REFERENCES "user" (id)]                                                                    
                             (Background on this error at: https://sqlalche.me/e/20/f405)Traceback (most recent call last):  

I've experienced this on several of the recent LangFlow versions (starting I think around 1.0.19).

Interestingly, it's saying it's trying to upgrade, but the data directories are totally clear.

Detailed log is here:
docker-compose-postgres-alembic2.log

Reproduction

1. Start LangFlow with this docker-compose.yaml file:

version: "0.4.12"

networks:
  langflow-network:
    driver: bridge

services:
  langflow3:
    image: langflowai/langflow-ep:v1.1.1.dev11 
    ports:
      - "7860:7860"
    command: ["langflow", "run", "--env-file", "/app/.env", "--host", "0.0.0.0", "--port", "7860"]
    working_dir: /app
    environment:
      - LANGFLOW_DATABASE_URL=postgresql://langflow:langflow@postgres:5432/langflow
      - COLUMNS=200
    volumes:
      - ./langflow-tmp/langflow-data:/app/langflow
      - ./langflow-tmp/langflow-app-data:/app/data
      - ./langflow-tmp/cache:/app/data/.cache
    networks:
      - langflow-network

  postgres:
    image: postgres:16
    environment:
      POSTGRES_USER: langflow
      POSTGRES_PASSWORD: langflow
      POSTGRES_DB: langflow
    ports:
      - "5432:5432"
    volumes:
      - ./langflow-tmp/langflow-postgres:/var/lib/postgresql/data
    networks:
      - langflow-network

Expected behavior

LangFlow should start as expected

Who can help?

@Jord

Operating System

Mac M1

Langflow Version

langflowai/langflow-ep:v1.1.1.dev11

Python Version

3.10

Screenshot

No response

Flow File

No response

[dosubot]

To resolve the startup crash in LangFlow with Postgres due to the "fk_flow_user_id_user" constraint already existing, you can modify the Alembic migration script to check for the existence of the foreign key constraint before attempting to create it. Here's a snippet that includes such a check:

flow_fks = {fk["name"] for fk in inspector.get_foreign_keys("flow")}

with op.batch_alter_table("flow", schema=None) as batch_op:
    if "flow_user_id_fkey" not in flow_fks:
        batch_op.create_foreign_key("flow_user_id_fkey", "user", ["user_id"], ["id"])

This modification ensures that the script checks for the existence of the foreign key constraint directly, preventing the attempt to create it if it already exists. Make sure to replace any outdated constraint names with the correct ones used in your database schema, such as "flow_user_id_fkey" instead of "fk_flow_user_id_user" ^[1][2].

To continue talking to Dosu, mention @dosu.

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[AQK99]

Hi, @ogabrielluiz I see that you worked last in the alembic. I'm getting the same issue. could you give some insight?

I'm not starting langflow from the docker, i'm trying to run it locally, and added the url to the .env file

[AQK99]

@devinbost I was able to fix this by updating the upgrade() function in /langflow/src/backend/base/langflow/alembic/versions/b2fa308044b5_add_unique_constraints.py to this:

def upgrade() -> None:
    # ### commands auto generated by Alembic - please adjust! ###
    conn = op.get_bind()
    inspector = sa.inspect(conn)  # type: ignore
    tables = inspector.get_table_names()
    # ### commands auto generated by Alembic - please adjust! ###
    try:
        if "flowstyle" in tables:
            op.drop_table("flowstyle")
        with op.batch_alter_table("flow", schema=None) as batch_op:
            flow_columns = [column["name"] for column in inspector.get_columns("flow")]
            if "is_component" not in flow_columns:
                batch_op.add_column(sa.Column("is_component", sa.Boolean(), nullable=True))
            if "updated_at" not in flow_columns:
                batch_op.add_column(sa.Column("updated_at", sa.DateTime(), nullable=True))
            if "folder" not in flow_columns:
                batch_op.add_column(sa.Column("folder", sqlmodel.sql.sqltypes.AutoString(), nullable=True))
            if "user_id" not in flow_columns:
                batch_op.add_column(sa.Column("user_id", sqlmodel.sql.sqltypes.types.Uuid(), nullable=True))
            indices = inspector.get_indexes("flow")
            indices_names = [index["name"] for index in indices]
            if "ix_flow_user_id" not in indices_names:
                batch_op.create_index(batch_op.f("ix_flow_user_id"), ["user_id"], unique=False)
            existing_fks = [fk["name"] for fk in inspector.get_foreign_keys("flow")]
            if "fk_flow_user_id_user" not in existing_fks:
                batch_op.create_foreign_key("fk_flow_user_id_user", "user", ["user_id"], ["id"])

    except Exception as e:
        logger.exception(f"Error during upgrade: {e}")
        pass
        ```